Improving the RIB 70 Jouef (2)

Mechanical changes (continued)

Concerning intermediate couplings, I initially used very much modified
Ribu boxes, but the result was not satisfactory because the elongation
kinematics was no longer respected and the return springs had become
traction springs so that the train played the accordion in acceleration,
all the more since the driver car opposed a considerable running
resistance, with its current pickup strips. So, I then decided to use
large size Makette drawbars.

But using NEM boxes was not possible because it was prevented by the
very forward and also too low position of the drawbars (because of the
bogies). It was also necessary to ensure the train’s electrical
continuity.

I first tried a complicated system of double connector extensions,
which would have made it possible to turn a car without reversing its
polarity. But it was useless for such a train whose composition in
service is normally immutable.

So, I imagined cutting the NEM boxes that had become useless and
replace them with a brass tube long enough to ensure the cars rubber
gangway connectors junction. Here is the fruit of this cogitation…

NB: if you are interested in knowing what I tried with the Ribu
drawbars, you can consult this page.

Makette drawbars

So, I tried a 3 x 6 mm rectangular brass tube coupling, which
will be relatively simple to make. Here are two aspects of it:

The tubes, longer than NEM boxes, make it possible to avoid an
intermediate part. In addition, their internal height (2.4 mm)
allows very little machining to insert a 2.54 mm pitch tulip
connector.

The problem of locking is solved with a bronze wire loop. This loop
was initially placed under the boxes. In use, I found that it was
better to place it at the top, because it thus prevents the couplings
from bending during the coupling.

Note: I had first tried with a square tube and a
single centred contact, the tube acting as the second pole. But this
solution posed a certain number of problems: short circuits between the
base of the drawbar and the wheels, bad contact between the two boxes
facing each other.

Drawing of the coupling

Making

The brass tube is milled (ø 6 milling bit) across every
12 mm to a 2 mm depth. Milling is required for each half
coupling. The tube is held between two 10 mm thick plywood jaws
which have been grooved together with the same ø 6 milling bit,
to a 2 mm depth. When machining, the wood is notched, but it does
not matter.

After turning the tube upside down, the locking grooves can be
milled, every two boxes. For this, I use a PCB engraving milling
bit.

Finally, the tube is cut with a “Bocfil” saw in 12 mm lengths,
then rectified to 10.5 mm with the milling machine to obtain the
dimensions indicated above.